Line pressure valve to selectively control distribution of pressurized fluid

ABSTRACT

A line pressure valve includes a valve housing having a central cavity and a plurality of inlet and outlet ports, and a spool positioned within the central cavity and axially displaceable therein, the spool having a plurality of radial cutouts that fluidly connect respective inlet and outlet ports based on an axial position of the spool with respect to the valve housing. First and second pumps are fluidly connectable and disconnectable respectively to and from the fluid circuit based on the axial position of the spool via the inlet and outlet ports.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/553,491, filed on Jul. 19, 2012, which is acontinuation-in-part of U.S. patent application Ser. No. 13/279,939,filed on Oct. 24, 2011, and this application claims priority toProvisional Patent Application 62/140,577 filed Mar. 31, 2015, which arehereby incorporated by reference in their entirety.

BACKGROUND

A hydraulic system may include a variety of hydraulically actuatedcomponents, each of which may have different flow and pressurerequirements that can vary over time. The hydraulic system may include apump for supplying a flow of pressurized fluid to the hydrauliccomponents. The pump may have a variable or fixed displacementconfiguration. Fixed displacement pumps are generally smaller, lighter,and less expensive than variable displacement pumps. Generally speaking,fixed displacement pumps deliver a finite volume of fluid for each cycleof pump operation. The output volume of a fixed displacement pump can becontrolled by adjusting the speed of the pump. The pump may be sized tosatisfy a maximum flow requirement of the hydraulic system. Closing orotherwise restricting the outlet of a fixed displacement pump willgenerally cause a corresponding increase in the system pressure. Toavoid over pressurizing the hydraulic system, fixed displacement pumpstypically utilize a pressure regulator or an unloading valve to controlthe pressure level within the system during periods in which the pumpoutput exceeds the flow requirements of the hydraulic components. Thepressure regulator or unloading valve operates to redirect the excessfluid back to a hydraulic system sump to be re-pressurized by the pump.This method of controlling system pressure and flow may result in asignificant reduction in the operating efficiency of the hydraulicsystem depending on the duration and magnitude of excess pump flow. Thehydraulic system may further include various valves for controlling thedistribution of the pressurized fluid to various hydraulic components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary hydraulic systememploying dual pumps for supply pressurized fluid to a high-pressurecircuit and a low-pressure circuit;

FIG. 2 is a schematic illustration of the exemplary hydraulic system ofFIG. 1 operating in a first operating mode;

FIG. 3 is a schematic illustration of the exemplary hydraulic system ofFIG. 1 operating in a second operating mode; and

FIG. 4 is a schematic illustration of the exemplary hydraulic system ofFIG. 1 operating in a third operating mode.

FIG. 5 is a schematic illustration of the exemplary hydraulic system ofFIG. 1 operating in a fourth operating mode.

FIG. 6 is a schematic illustration of the exemplary hydraulic system ofFIG. 1 operating in a fifth operating mode.

FIG. 7 is a schematic illustration of a line pressure valvecorresponding to FIGS. 1 and 2 and having respective inlet and outletlines illustrated, and having all ports closed.

FIG. 8A is an illustration of the line pressure valve of FIG. 7 havingall ports close, corresponding to FIGS. 1 and 2.

FIG. 8B is an illustration of the line pressure valve of FIG. 7, havingthe spool positioned in a first intermediate position in which flow isbeginning to occur, corresponding to FIG. 5.

FIG. 8C is an illustration of the line pressure valve of FIG. 7, havingthe spool positioned at a second position that corresponds to FIG. 3.

FIG. 8D is an illustration of the line pressure valve of FIG. 7, havingthe spool positioned corresponding to FIG. 6 in a second intermediateposition.

FIG. 8E is an illustration of the line pressure valve of FIG. 7, havingthe spool positioned at a third position that corresponds to FIG. 4.

FIG. 8F is an illustration of the line pressure valve of FIG. 7, havingthe spool positioned “wide open” and corresponding also to FIG. 4.

FIG. 9A illustrates flow metering notches positioned in a spool.

FIG. 9B illustrates flow metering notches positioned in a housing.

DETAILED DESCRIPTION

Referring now to the discussion that follows and the drawings,illustrative approaches to the disclosed systems and methods aredescribed in detail. Although the drawings represent some possibleapproaches, the drawings are not necessarily to scale and certainfeatures may be exaggerated, removed, or partially sectioned to betterillustrate and explain the present disclosure. Further, the descriptionsset forth herein are not intended to be exhaustive, otherwise limit, orrestrict the claims to the precise forms and configurations shown in thedrawings and disclosed in the following detailed description.

FIG. 1 schematically illustrates an exemplary pressurized fluiddistribution system 10 operable for selectively distributing apressurized fluid to various hydraulically actuated components. Fluiddistribution system 10 may have various configurations depending on therequirements of a particular application. For example, the exemplaryfluid distribution systems illustrated in FIGS. 1-6 are configured foruse in automotive transmission applications. The illustrated fluiddistribution systems operate to distribute pressurized fluid for use inactivating clutches, initiating gearshifts, and providing clutch coolingand lubrication, as well as providing other functions.

Fluid distribution system 10 may include multiple hydraulic circuits forselectively distributing the pressurized fluid to various hydraulicallyactuated components associated with the respective hydraulic circuits.Fluid distribution system 10 may generally include a high-pressurecircuit having a high-pressure fluid passage 52 and a low-pressurecircuit having a low-pressure fluid passage 108, although in practicefewer or more hydraulic circuits may be provided depending on therequirements of a particular application. Pressurized fluid distributedby the high-pressure circuit may be used, for example, to actuatehydraulic components that generally have high pressure and low flowrequirements, such as primary clutch actuator 12, secondary clutchactuator 14 and shift rail actuators 16. Pressurized fluid distributedby the low-pressure circuit may provide lubrication for bearings,including, for example, various transmission bearings 18, main caseintermediate wall bearings 20 and rear case bearings 22, and providecooling of clutches, such as primary clutch 24 and secondary clutch 26.The pressurized fluid from the low-pressure circuit may also bedischarged through spray bar 28 to provide lubrication for transmissiongears. Lubrication and cooling functions typically have higher flow andlower pressure requirements than other functions, such as clutch andshift rail actuation.

The terms high-pressure circuit and low-pressure circuit merely identifythe respective fluid circuits for purposes of discussion, and are notintended to denote an actual pressure level that may occur within therespective fluid circuits, or that the high-pressure circuit will alwaysoperate at a higher pressure level than the low-pressure circuit.Although, the high-pressure circuit generally operates at a higherpressure level than the low pressure circuit, there may be certainoperating conditions under which the pressure level within thelow-pressure circuit approaches or exceeds that of the high pressurecircuit. It is not necessary that the high-pressure circuit continuallyoperate at a higher pressure than the low-pressure circuit under alloperating conditions.

With continued reference to FIG. 1, a pump assembly 30 may providepressurized fluid for distribution by the high-pressure circuit and thelow-pressure circuit. Pump assembly 30 may include one or more pumps.The illustrated exemplary configuration includes two pumps, butadditional pumps may also be employed depending on the design andperformance requirements of a particular application. Pump assembly 30may include a first pump 32 and a second pump 34. First pump 32 andsecond pump 34 may be selectively fluidly connected, either individuallyor in combination, to the high-pressure circuit and the low-pressurecircuit depending on the flow requirements of the particular fluidcircuit. Generally the output flow from second pump 34 will be directedto the low-pressure circuit to provide lubrication for gears andbearings, and cooling for clutches, whereas the output flow from firstpump 32 will be directed to the high-pressure circuit for actuatingshift rails and clutches. Certain operations, however, such as clutchactuation and shift rail actuation, may include brief periods duringwhich the flow requirement of the high-pressure circuit exceeds the flowoutput of first pump 32. The additional flow may be satisfied bytemporarily directing at least a portion of the fluid output from secondpump 34 to the high-pressure circuit. During this period, at least aportion of the fluid flow from second pump 34 may be diverted away fromthe low-pressure circuit. Once the excess flow requirement of thehigh-pressure circuit has abated, the diverted flow from second pump 34may once again be directed to the low-pressure circuit. There may alsobe periods during which the flow requirement of the high-pressurecircuit is less than the flow output of first pump 32. During theseperiods at least a portion of the excess flow output from first pump 32may be directed to the low-pressure circuit. When the flow requirementof the high-pressure circuit increases the flow from first pump 32 maybe redirected back to the high-pressure circuit.

First pump 32 may be mounted to a first drive shaft 36 and second pump34 may be mounted to a second drive shaft 38. First drive shaft 36 maybe fixedly connected to second drive shaft 38 via a coupling 40 toenable first pump 32 and second pump 34 to rotate in unison, and thus beoperated at substantially the same speed (e.g., revolutions per minute(rpm)). Alternatively, first drive shaft 36 and second drive shaft 38may be interconnected via a suitably configured gear box 42 to enablethe first and second pumps to rotate at a selected fixed speed ratiorelative to one another. First drive shaft 36 and second drive shaft 38may also be integrated as a single shaft. First drive shaft 36 andsecond drive shaft 38 may be connected to an external power source 44,such as an engine, electric motor, or other power source capable ofoutputting a rotational torque. An inlet port 46 of first pump 32 and aninlet port 48 of second pump 34 may be fluidly connected to a fluid sump50 that provides a source of hydraulic fluid for the pumps.

First pump 32 and second pump 34 may include any of a variety of knownfixed displacement pumps, including but not limited to, gear pumps, vanepumps, axial piston pumps, and radial piston pumps. The pumps may besubstantially the same size, or have a different size. The size of afixed displacement pump may be defined in terms of its fluid output ratewhen operated at a particular speed (e.g., revolutions per minute(rpm)). Increasing the size of the pump generally produces acorresponding increase in the fluid output rate of the pump. Forexample, a first pump capable of outputting 5 Liters/minute whenoperated at a speed of 1000 rpm is considered to be smaller than asecond pump capable of outputting 6 Liters/minute when operated at thesame speed. First pump 32 will generally be sized smaller than secondpump 34 (i.e., produce a lower flow output at a given operating speed)due to the high pressure circuit typically having lower flow and higherpressure requirements than the low pressure circuit. In practice, firstpump 32 may be sized larger than second pump 34, or both pumps may havesubstantially the same size. First pump 32 and second pump 34 may beoperated at substantially the same speed.

Continuing to refer to FIG. 1, the high-pressure circuit may include ahigh-pressure fluid passage 52 fluidly connected to a discharge port 54of first pump 32. Pressurized fluid output from first pump 32 may bedirected through high-pressure fluid passage 52 to an actuation controlmanifold 56 (ACM), which operates to direct the pressurized fluid to thedesired hydraulic components, for example, shift rail actuators 16,primary clutch actuator 12 and secondary clutch actuator 14.

With continued reference to FIG. 1, a line-pressure valve 58 (LPV) maybe provided to selectively control distribution of pressurized fluidfrom first pump 32 and second pump 34 between the high-pressure circuitand the low-pressure circuit. This may enable more efficient use of thepumps and enable the pumps to be sized smaller than generally would berequired if each pump were sized to satisfy the maximum flow requirementof the respective fluid circuit. Smaller pumps generally require lesspower to operate than larger pumps. For example, first pump 32 andsecond pump 34 may be sized to accommodate the pressure and flowrequirements predominantly occurring within the respective high pressurecircuit and low pressure circuit, which is typically less, and may besignificantly less, than the respective fluid circuit's maximum pressureand flow requirement. During instances in which the flow and/or pressurerequirement of a particular fluid circuit exceeds the output of thecorresponding pump, at least a portion of the fluid from the pumpsupplying the other fluid circuit may be temporarily diverted to thefluid circuit requiring the additional flow to satisfy the deficiency.Once the excess flow requirement has subsided, the additional flow maybe redirected back to the other fluid circuit. The ability toselectively distribute the fluid output from first pump 32 and secondpump 34 may allow the use of smaller pumps having lower powerconsumption, which may increase the overall efficiency of the fluiddistribution system.

Line-pressure valve 58 may be configured as a pilot controlled three-wayfour-port valve having a high-pressure inlet port 60, a low-pressureinlet port 62, a high-pressure discharge port 64 and a low-pressuredischarge port 66. Line-pressure valve 58 may be operated to selectivelyfluidly connect low-pressure inlet port 62 to low pressure dischargeport 66, and to selectively fluidly connect high pressure inlet port 60to high-pressure discharge port 64. Although line-pressure valve 58 isillustrated as a pilot controlled three-way four-port valve, it shall beappreciated that other valve configurations may also be used dependingon the particular application.

Line-pressure valve 58 may be fluidly connected to first pump 32 througha high-pressure supply passage 68 fluidly connecting high-pressure inletport 60 of line-pressure valve 58 to high-pressure fluid passage 52.Line-pressure valve 58 may be fluidly connected to second pump 34 by wayof a low-pressure supply passage 70 fluidly connecting a discharge port72 of second pump 34 to low-pressure inlet port 62 of line-pressurevalve 58.

To control distribution of pressurized fluid from first pump 32 andsecond pump 34 between the high-pressure and low-pressure circuits,line-pressure valve 58 may be selectively arranged in any of threepositions 74, 76 and 78. Line-pressure valve 58 is illustrated arrangedin first position 74 in FIGS. 1 and 2, in second position 76 in FIG. 3,and in third position 78 in FIG. 4. Arranging line-pressure valve 58 infirst position 74 substantially blocks pressurized fluid from flowingbetween low-pressure inlet port 62 and low-pressure discharge port 66,and between high-pressure inlet port 60 and high pressure-discharge port64. Arranging line-pressure valve 58 in second position 76 fluidlyconnects low-pressure inlet port 62 to low-pressure discharge port 66,while substantially blocking the flow of fluid between high-pressureinlet port 60 and high-pressure discharge port 64. Arrangingline-pressure valve 58 in third position 78 fluidly connectslow-pressure inlet port 62 to low-pressure discharge port 66 andhigh-pressure inlet port 60 to high pressure discharge port 64.

Line-pressure valve 58 may also be configured for variable output, whichmay be enabled by arranging line-pressure valve 58 at one or moreintermediate positions 71, 73 between first position 74 and thirdposition 78. For example, arranging line-pressure valve 58 between firstposition 74 and second position 76 fluidly connects low-pressure inletport 62 to low-pressure discharge port 66 and substantially blocks theflow of fluid between high-pressure inlet port 60 and high-pressuredischarge port 64. Arranging line-pressure valve 58 between firstposition 74 and second position 76 restricts fluid flow betweenlow-pressure inlet port 62 and low pressure discharge port 66 tosomething less than would occur with the valve is arranged in secondposition 76. The fluid flow path between low-pressure inlet port 62 andlow-pressure discharge port 66 is substantially fully open whenline-pressure valve 58 is arranged in second position 76, and issubstantially closed when the valve is arranged in first position 74.The fluid flow path between low-pressure inlet port 62 and low-pressuredischarge port 66 generally becomes more restrictive as line-pressurevalve 58 is moved away from second position 76 and toward first position74. Generally the fluid flow path between high-pressure inlet port 60and high-pressure discharge port 64 remains substantially blocked overthe entire range between and including first position 74 and secondposition 76.

Arranging line-pressure valve 58 between second position 76 and thirdposition 78 restricts fluid flow between high-pressure inlet port 60 andhigh-pressure discharge port 64 to something less than when the valve isarranged in third position 78. The fluid flow path between high-pressureinlet port 60 and high-pressure discharge port 64 is substantially fullyopen when line-pressure valve 58 is arranged in third position 78, andis substantially closed when the valve is arranged in second position76. The fluid flow path between high-pressure inlet port 60 andhigh-pressure discharge port 64 generally becomes less restrictive asline-pressure valve 58 is moved away from second position 76 and towardthird position 78. Generally the fluid flow path between low-pressureinlet port 62 and low-pressure discharge port 66 remains substantiallyfully open over the entire range between and including second position76 and third position 78.

With continued reference to FIG. 1, a biasing member 80 biasesline-pressure valve 58 toward first position 74, which is the defaultposition. A pressure tap 82 may be provided to detect a pressure levelwithin high-pressure supply passage 68. Pressure tap 82 provides a pilotpressure that tends to move line-pressure valve 58 away from firstposition 74 and toward third position 78.

A pilot pressure signal for controlling operation of line-pressure valve58 may be transmitted from actuation control manifold 56 and deliveredto line-pressure valve 58 through a pilot signal passage 84. The pilotsignal operates in conjunction with biasing member 80 to moveline-pressure valve 58 toward first position 74 and away from thirdposition 78. Line-pressure valve 58 will generally not begin to moveback toward first position 74 and away from third position 78 until thepilot pressure supplied by pressure tap 82 exceeds the combined biasingforce exerted by biasing member 80 and supplied by pilot signal passage84.

The pilot signal may be controlled by a line pressure solenoid valve 86(LPS), which operates to generate the pilot signal by selectivelyfluidly connecting pilot signal passage 84 to high-pressure fluidpassage 52 through a pilot pressure supply passage 88. Line pressuresolenoid valve 86 may be configured as a three-way two-position valve,and may be selectively arranged in a first position 90 for fluidlyconnecting pilot pressure supply passage 88 to pilot signal passage 84,and a second position 92 for fluidly connecting pilot signal passage 84to fluid sump 50.

Line pressure solenoid valve 86 may be configured for variable output byarranging the valve at one or more intermediate positions between firstposition 90 and second position 92. A biasing member 94 may be providedto bias line pressure solenoid valve 86 toward first position 90, whichis the default position. A pressure tap 96 may also be provided todetect a pressure level within pilot signal passage 84. Pressure tap 96provides a pilot pressure that operates in conjunction with biasingmember 94 to bias line pressure solenoid valve 86 toward first position90.

Line pressure solenoid valve 86 may include a solenoid 98 selectivelyoperable to bias line pressure solenoid valve 86 toward second position92 and away from first position 90 in response to a signal received froma controller, such as, for example, a transmission control module (TCM)or a transmission control unit (TCU). Solenoid 98 may be configured as avariable force solenoid or a variable bleed solenoid, by way of example.Activating solenoid 98 biases line pressure solenoid valve 86 towardsecond position 92 and away from first position 90. Line pressuresolenoid valve 86 will generally be arranged in the default firstposition 90 when solenoid 98 is deactivated.

With continued reference to FIG. 1, second pump 34 may be selectivelyfluidly connected to high-pressure fluid passage 52 by way of a blockingactuation passage 100. One end of blocking actuation passage 100 may befluidly connected to low-pressure supply passage 70 upstream ofline-pressure valve 58 at a fluid junction 102, and an opposite endfluidly connected to high-pressure fluid passage 52 at a fluid junction104. Blocking actuation passage 100 may include a blocking actuationcheck valve 106 (BACV) operable to substantially block fluid presentwithin the high-pressure circuit from flowing through blocking actuationpassage 100 to low-pressure supply passage 70 under all operatingconditions and regardless of the positioning of line-pressure valve 58.Blocking actuation check valve 106 may be configured to allowpressurized fluid from second pump 34 to pass through the valve to thehigh-pressure circuit when a predetermined pressure drop across blockingactuation check valve 106 is exceeded. The pressure drop being such thatthe pressure within low-pressure supply passage 70 is greater than thepressure within high-pressure fluid passage 52. Blocking actuation checkvalve 106 may be configured as a check valve.

Blocking actuation check valve 106 may be configured to be infinitelymoveable between a fully closed position, in which fluid output fromsecond pump 34 is substantially blocked from passing through the valveto high-pressure fluid passage 52, and a fully open position, in whichsubstantially all or a portion of the fluid output from second pump 34is allowed to pass through the valve to high-pressure fluid passage 52.Blocking actuation check valve 106 may be configured to operate inresponse to a pressure drop occurring across the check valve. Forexample, blocking actuation check valve 106 may be configured tocommence opening at a predetermined minimum pressure drop occurringacross the valve. Further increasing the pressure drop causes blockingactuation check valve 106 to further open, thereby increasing the flowrate through the valve from low-pressure supply passage 70 tohigh-pressure fluid passage 52.

Arranging line-pressure valve 58 in either second position 76 or thirdposition 78 allows pressurized fluid from second pump 34 to flow to thelow-pressure circuit through a low-pressure fluid passage 108, which maybe fluidly connected to high-pressure discharge port 64 and low-pressuredischarge port 66 of line-pressure valve 58. Low-pressure fluid passage108 may be fluidly connected to an inlet port 110 of a heat exchanger112. Heat exchanger 112 may include various configurations, includingbut not limited to, a water to oil heat exchanger. When configured as awater to oil heat exchanger, a portion of the heat contained within thepressurized fluid passing through heat exchanger 112 may be transferredto water flowing over the heat exchanger.

A heat exchanger discharge passage 114 may be fluidly connected to adischarge port 116 of heat exchanger 112. A heat exchanger bypasspassage 118 may be provided to allow the pressurized fluid to bypassheat exchanger 112, should the heat exchanger become clogged orotherwise restrict the flow of fluid through the heat exchanger. Heatexchanger bypass passage 118 may include a heat exchanger check valve120 (HECV) for limiting a pressure drop across heat exchanger 112. Heatexchanger check valve 120 senses a pressure drop across heat exchanger112 and may be configured to open when the pressure drop exceeds apredetermined magnitude.

Pressurized fluid discharged from heat exchanger 112 may be used toprovide lubrication for bearings 18, 20 and 22, and delivered to spraybar 28 for lubricating gears. Pressurized fluid not used for bearing andgear lubrication may provide cooling for a primary clutch 24 and asecondary clutch 26. Pressurized fluid for clutch cooling may bediverted to primary clutch 24 and secondary clutch 26 through a clutchcooling supply passage 122 fluidly connected to heat exchanger dischargepassage 114 at a fluid junction 124.

Distribution of pressurized fluid between primary clutch 24 andsecondary clutch 26 may be selectively controlled by a clutch coolingprimary valve 126 (CCPV) and a clutch cooling secondary valve 128(CCSV). Clutch primary cooling valve 126 may be fluidly connected toclutch cooling supply passage 122 through a CCPV supply passage 130.Clutch secondary cooling valve 128 may be fluidly connected to clutchcooling supply passage 122 through a CCSV supply passage 132. Clutchcooling primary valve 126 is operable to control the flow of pressurizedcooling fluid to primary clutch 24, and clutch cooling secondary valve128 is operable to control the flow of pressurized cooling fluid tosecondary clutch 26.

Clutch cooling primary valve 126 may be configured as a pilot actuatedthree-position five-port valve. A biasing member 134 biases clutchcooling primary valve 126 to a default first position 136, in whichcooling fluid from primary clutch 26 is allowed to flow back throughclutch cooling primary valve 126 and is returned to fluid sump 50.Clutch cooling primary valve 126 is illustrated in FIGS. 1-4 in thedefault first position 136. Clutch cooling primary valve 126 may also bearranged in an intermediate second position 138, in which pressurizedfluid flows through a calibrated orifice 140 to primary clutch 24through a primary clutch cooling supply passage 142. Clutch coolingprimary valve 126 may be arranged in a third position 144, in whichpressurized fluid is allowed to flow to primary clutch 24 throughcalibrated orifice 140 and primary clutch cooling supply passage 142.Third position 144 provides a higher flow rate than second position 138,in which fluid is allowed to flow only through calibrated orifice 140. Apilot pressure signal for controlling operation of clutch coolingprimary valve 126 may be provided by a primary clutch actuation pressurereceived from actuation control manifold 56 and delivered to the valvethrough a pilot signal passage 146.

Clutch cooling secondary valve 128 may be configured as a pilot actuatedthree-position five-port valve. A biasing member 148 biases clutchcooling secondary valve 128 to a default first position 150, in whichcooling fluid from secondary clutch 26 is allowed to flow back throughclutch cooling secondary valve 128 and is returned to fluid sump 50.Clutch cooling secondary valve 128 is illustrated in the default firstposition 150 in FIGS. 1-6. Clutch cooling secondary valve 128 may alsobe arranged in an intermediate second position 152, in which pressurizedfluid flows through a calibrated orifice 154 to secondary clutch 26through a secondary clutch cooling supply passage 156. Clutch coolingsecondary valve 128 may be arranged in a third position 158, in whichpressurized fluid is allowed to flow to secondary clutch 26 throughorifice 154 and secondary clutch cooling supply passage 156. Thirdposition 158 provides a higher flow rate than second position 152, inwhich fluid is only allowed to flow through calibrated orifice 154. Apilot pressure signal for controlling operation of clutch coolingsecondary valve 128 may be transmitted from actuation control manifold56 and delivered to the valve through a pilot signal passage 160.

Continuing to refer to FIG. 1, to limit a maximum pressure occurringwithin the fluid circuit upstream of line-pressure valve 58,particularly when line-pressure valve 58 is arranged in first position74, a relief valve 162 may be provided to selectively direct at least aportion of pressurized fluid from the circuit back to first pump 32 andsecond pump 34. Relief valve 162 may be disposed in a fluid path of arelief passage 164 that fluidly connects low-pressure supply passage 70to inlet port 48 of second pump 34 and inlet port 46 of first pump 32.Relief valve 162 is operable to substantially block fluid from passingfrom first pump 32 and second pump 34 through relief valve 162 tolow-pressure supply passage 70 under all operating conditions. Reliefvalve 162 may be configured to allow pressurized fluid from low-pressuresupply passage 70 to pass through the valve to first pump 32 and secondpump 34 when a predetermined pressure drop across relief valve 162 isexceeded.

Relief valve 162 may be configured to be infinitely moveable between afully closed position, in which fluid from low-pressure supply passage70 is substantially blocked from passing through the valve to first pump32 and second pump 34, and a fully open position in which substantiallyall or a portion of fluid passing through low-pressure supply passage 70is allowed to pass through the valve to first pump 32 and second pump34.

Relief valve 162 may be configured to operate in response to a pressuredrop occurring across the valve. For example, relief valve 162 may beconfigured to commence opening at a predetermined minimum pressure dropoccurring across the valve. Further increasing the pressure drop causesrelief valve 162 to further open, thereby increasing the flow ratethrough the valve from low-pressure supply passage 70 to first pump 32and second pump 34.

Continuing to refer to FIG. 1, a clutch backpressure valve 166 (CBV) maybe provided to limit a maximum pressure that may occur within thelow-pressure circuit. Clutch backpressure valve 166 is operable toselectively direct at least a portion of pressurized fluid from thelow-pressure circuit back to first pump 32 and second pump 34 when thepressure within the low-pressure circuit exceeds a predetermined limit.Clutch backpressure valve 166 may be disposed in the fluid path of aclutch backpressure relief passage 168 fluidly connecting heat exchangerinlet port 110 to inlet port 48 of second pump 34 and inlet port 46 offirst pump 32. Clutch backpressure valve 166 may be configured tooperate in response to a detected pressure within clutch backpressurerelief passage 168. For example, clutch backpressure valve 166 may beconfigured to commence opening when the pressure within clutchbackpressure relief passage 168 exceeds a predetermined limit. Furtherincreasing the pressure within clutch backpressure relief passage 168causes clutch backpressure valve 166 to further open. On the other hand,decreasing the pressure within clutch backpressure relief passage 168causes the valve to commence closing to reduce the flow of pressurizedfluid.

Operation of pressurized fluid distribution system 10 will now bedescribed with reference to FIGS. 2-6. Pressurized fluid distributionsystem 10 may generally operate in three different operating modes. Afirst operating mode has pressurized fluid from first pump 32 and secondpump 34 being directed away from the low-pressure circuit and deliveredto the high-pressure circuit. A second operating mode has pressurizedfluid from first pump 32 delivered to the high-pressure circuit andpressurized fluid from second pump 34 delivered to the low-pressurecircuit. A third operating mode has pressurized fluid from second pump34 and at least a portion of the pressurized fluid from first pump 32delivered to the low-pressure circuit. The first operating mode may beselected by arranging line-pressure valve 58 in first position 74. Thesecond operating mode may be selected by arranging line-pressure valve58 in second position 76. The third operating mode may be selected byarranging line-pressure valve 58 in third position 78. FIG. 2illustrates the fluid path traveled by the pressurized fluid whenoperating fluid distribution system 10 in the first operating mode. FIG.3 illustrates the fluid path traveled by the pressurized fluid whenoperating fluid distribution system 10 in the second operating mode.FIG. 4 illustrates the fluid path traveled by the pressurized fluid whenoperating fluid distribution system 10 in the third operating mode.

Arranging line-pressure valve 58 in the intermediate position 71 betweenfirst position 74 and second position 76 causes the fluid output fromsecond pump 34 to be apportioned between the high pressure circuit andthe low-pressure circuit and the entire fluid output from first pump 32to be delivered to the high-pressure circuit. Such an arrangementrepresents a fourth operating mode, as illustrated in FIG. 5. Arrangingline-pressure valve 58 in the intermediate position 73 between secondposition 76 and third position 78 causes the fluid output from firstpump 32 to be apportioned between the high pressure circuit and thelow-pressure circuit and the entire fluid output from second pump 34 tobe delivered to the low-pressure circuit. Such an arrangement representsa fifth operating mode, as illustrated in FIG. 6.

Arranging line-pressure valve 58 in first position 74 substantiallyblocks the flow of fluid between low-pressure supply passage 70 andlow-pressure fluid passage 108 and may cause substantially the entirefluid output from second pump 34 to travel from low-pressure supplypassage 70 through blocking actuation passage 100 to high-pressure fluidpassage 52 (as illustrated in FIG. 2). Arranging line-pressure valve 58in the intermediate position 71 between first position 74 and secondposition 76, as illustrated in FIG. 5, causes a portion of the pressuredfluid from second pump 34 to travel from low-pressure supply passage 70through blocking actuation passage 100 to high-pressure fluid passage52, and the remainder of the fluid to travel through line-pressure valve58 to the low-pressure circuit. Pressurized fluid from first pump 32 isdelivered to the high-pressure circuit through high-pressure fluidpassage 52 and blocked from being delivered to the low-pressure circuitwhen line-pressure valve 58 is arranged in any position between andincluding first position 74 and second position 76. Arrangingline-pressure valve 58 in second position 76 fluidly connectslow-pressure supply passage 70 to low-pressure fluid passage 108 whilesubstantially blocking the flow of fluid from high-pressure fluidpassage 52 to low-pressure fluid passage 108. Arranging line-pressurevalve 58 in third position 78 fluidly connects low-pressure supplypassage 70 and high-pressure fluid passage 52 to low-pressure fluidpassage 108, and causes at least a portion of the pressurized fluid fromfirst pump 32 to flow to the low-pressure circuit and the remainingportion to flow to the high-pressure circuit. Arranging line-pressurevalve 58 in the intermediate position 73 between second position 76 andthird position 78, as illustrated in FIG. 6, causes the entire fluidoutput from second pump 34 to be delivered to the low-pressure circuitand the fluid output from first pump 32 to be apportioned between thelow-pressure circuit and the high-pressure circuit.

Fluid distribution system 10 will generally operate in the secondoperating mode (FIG. 3) when the flow output from first pump 32 issufficient to satisfy the flow requirement of the high-pressure circuit.However, there may be instances in which the flow requirement of thehigh-pressure circuit temporarily exceeds the flow output of first pump32. When this occurs, fluid distribution system 10 may be operated inthe first operating mode (FIG. 2), or the intermediate fourth operatingmode between the first and second operating modes, in which at least aportion of the fluid output from second pump 34 is directed away fromthe low-pressure circuit and delivered to the high-pressure circuit tosatisfy the temporary excess flow requirement. The second operating modemay be reinitiated, and the flow output from second pump 34 directedback to the low-pressure circuit, when the excess flow requirement ofthe high-pressure circuit no longer exists.

Referring to FIG. 3, the second operating mode may be actuated byarranging line-pressure valve 58 in second position 76, which allowspressurized fluid from second pump 34 to pass through line-pressurevalve 58 to the low-pressure circuit. With line-pressure valve 58arranged in second position 76, the pressure within low-pressure supplypassage 70 of the low-pressure circuit will generally be lower than thepressure within high-pressure fluid passage 52 of the high-pressurecircuit. This generally results in a pressure delta across blockingactuation check valve 106 that is less than the predetermined pressuredelta required to open the check valve, thereby substantially preventingpressurized fluid from second pump 34 from flowing through blockingactuation passage 100 to the high-pressure circuit.

With reference to FIG. 2, the first operating mode may be actuated byarranging line-pressure valve 58 in first position 74, or in a fourthoperating mode when in the intermediate position 71 between firstposition 74 and second position 76, thereby blocking at least a portionof the flow of pressurized fluid from pump 34 to the low-pressurecircuit. Blocking actuation check valve 106 controls the flow of fluidfrom second pump 34 to the high-pressure circuit through blockingactuation passage 100 based on the arrangement of line-pressure valve58. Arranging line-pressure valve 58 in first position 74, or theintermediate position 71 between first position 74 and second position76, generally causes a corresponding increase in pressure withinlow-pressure supply passage 70. The pressure increase withinlow-pressure supply passage 70 required to transition from the secondoperating mode to the first operating mode may be achieved withouthaving to adjust the operating speed of first pump 32 and second pump34. This may cause the pressure within low-pressure supply passage 70 toexceed the pressure within high-pressure fluid passage 52 of thehigh-pressure circuit, resulting in a corresponding pressure deltaacross blocking actuation check valve 106. When the pressure deltaexceeds the predetermined pressure delta required to open blockingactuation check valve 106, the pressurized fluid from second pump 34will commence flowing through blocking actuation passage 100 to thehigh-pressure circuit, thereby providing additional fluid to satisfy thetemporary excess flow requirement of the high-pressure circuit.

With reference to FIG. 4, there may be instances in which the flowrequirement of the high-pressure circuit is less than the flow output offirst pump 32. When this occurs, fluid distribution system 10 may beoperated in the third operating mode (FIG. 4), or in a fifthintermediate operating mode between the second and third operatingmodes, in which at least a portion of the fluid output from first pump32 is directed away from the high-pressure circuit and delivered to thelow-pressure circuit. The second operating mode may be reinitiated, andthe flow output from first pump 32 directed back to the high-pressurecircuit, when the flow requirement of the high-pressure circuit againapproaches the flow output of first pump 32. The third operating modemay be actuated by arranging line-pressure valve 58 in third position78, or in an intermediate fifth operating mode when positioned betweensecond position 76 and third position 78, thereby redirecting at least aportion of the flow of pressurized fluid from first pump 32 to thelow-pressure circuit and away from the high-pressure circuit.

FIG. 7 shows details of a line pressure valve (LPV) 700, whichcorresponds to LPV 58 illustrated in FIGS. 1-6. LPV 700 is shown in thecontext of fluid distribution system 10 and includes, for referencepurposes, first pump 32, second pump 34, and BACV 106. LPV 700 includesa valve housing 702 and a spool 704. Valve housing 702 includes acentral cavity 706 in which spool 704 is positioned. Spool 704 isaxially positionable within central cavity 706, having features as willbe further described that selectively connect inlet and outlet portsduring a controlled operation of LPV 700.

LPV 700 includes, in fluid correspondence with second pump 34, a firstinlet port 708 and a second inlet port 710, as well as a first outletport 712 and a second outlet port 714. LPV 700 also includes, in fluidcorrespondence with first pump 32, an inlet port 716 and an outlet port718. Low pressure pump 34 (LP Pump) is fluidly connected to inlet port708 and to inlet port 710, and high pressure pump 32 (HP Pump) isfluidly connected to inlet port 716. Outlet ports 712, 714, and 718 arefluidly connectable to respective inlet ports 708, 710, and 716 viaspool 704 that is axially moveable to controllably open the connectionfrom inlets 708, 710, and 716 to respective outlets 712, 714, and 718.FIG. 7 illustrates a position of the spool corresponding to FIGS. 1 and2 above in which all ports are closed.

Inlet ports 708 and 710 correspond with low-pressure inlet port 62 ofthe above figures, while inlet port 716 corresponds with high-pressureinlet port 60. Outlet ports 712 and 714 correspond with low-pressureoutlet or discharge port 66 of the above figures, while outlet port 718corresponds with high-pressure outlet or discharge port 64. Accordingly,LPV 700, corresponding to line-pressure valve 58 as described above, maybe selectively operated in positions 74, 76, and 78 as described in thefigures above, and may also be selectively operated in intermediatepositions 71 and 73, as well. Spool 704 includes two radial cutouts 720,722 and valve housing 702 includes the two corresponding inlet ports708, 710.

In the following FIGS. 8A-8F, LPV 58 is shown having the spool atvarious positions. An amount of “stroke” varies progressively in thefollowing figures, corresponding to the axial displacement of the spool,which controllably opens access between respective inlet and outletports. In the example provided herein, the amount of stroke variesbetween 0.0 mm (ports fully closed) and 6.0 mm (ports as open aspossible). The stroke ranging from 0.0-6.0 mm is merely exemplary andprovided for discussion purposes such that the amount of relative strokemay be discussed, however it is contemplated that the disclosed valveand its operation may be used in any size or corresponding amount ofstroke, having the function as disclosed herein. Also, inlets, outlets,and other components are identified, where relevant for discussion, asthey pertain to the element markings of FIG. 7.

FIG. 8A indicates the first position, with spool at rest, and all portsclosed (Stroke at 0.0 mm), corresponding to FIGS. 1 and 2. FIG. 8Acorresponds to the spool in the same position as shown in FIG. 7 above,as well. Accordingly, spool 704 is axially positioned such that inletports 708, 710 are blocked by outer circumferences 802, 804 of spool 704at their respective locations, and inlet port 716 likewise is blocked byouter circumference 806 at its location, as well. Accordingly, inletlines from each pump 34, 32 are blocked as shown also in FIGS. 1 and 2.

FIG. 8B is an illustration of the line pressure valve of FIG. 7, havingspool 704 positioned at a first intermediate position between first andsecond positions in which flow is beginning to occur (Stroke at 1.5 mm),corresponding to FIG. 5 and at position 71. In this case inlet ports708, 710 are connected line-to-line (just about to open to outlet ports712, 714) and fluid is just starting to flow in this position, whileinlet port 716 is still closed, and corresponds with the fourthoperating mode.

FIG. 8C indicates a second position, with inlet ports 708, 710 openwhile inlet port 716 is still closed (Stroke at 2.0 mm). This positioncorresponds with second operating mode illustrated in FIG. 3, in whichLPV 58 is in position 76.

FIG. 8D is an illustration of the line pressure valve of FIG. 7, havingspool 704 positioned corresponding to FIG. 6 in a second intermediateposition that corresponds with position 73. Inlet ports 708, 710 areopen more than in FIGS. 8A-8C, and inlet port 716 is line-to-line (aboutto open, stroke at 3.0 mm), in which fluid flow is about to occur.

FIG. 8E indicates a third position. Inlet ports 708, 710 are open morethan in the previous FIGS. 8A-8D, and inlet port 716 is opened enough toalmost be stroked beyond a flow metering notch (discussed below). Strokein this exemplary valve is 4.0 mm. This position corresponds with thirdoperating mode illustrated in FIG. 4, in which LPV 58 is at thirdposition 78.

FIG. 8F indicates a third position that also corresponds with FIG. 4,but stroke in this exemplary valve is 6.0 and all valves are wide open.

Accordingly, pump 32 is fluidly disconnected from the fluid circuit whenspool 704 is arranged in a first position (FIGS. 1 and 2, and FIG. 8A),a second position (FIG. 3 and FIG. 8C), and a first intermediateposition (FIG. 5 and FIG. 8B) between the first and second positions,and pump 32 is fluidly connected to the fluid circuit when spool 704 isarranged in a third position (FIG. 4 and FIG. 8E) and a secondintermediate position (FIG. 6 and FIG. 8D) between the second and thirdpositions. Pump 34 is fluidly disconnected from the fluid circuit whenspool 704 is arranged in the first position (FIGS. 1 and 2, and FIG.8A), and pump 34 is fluidly connected to the fluid circuit when spool704 is arranged in the second position FIG. 3 and FIG. 8C), the thirdposition (FIG. 4 and FIG. 8E), first intermediate position (FIG. 5 andFIG. 8C), and the second intermediate position (FIG. 6 and FIG. 8E).

Spool 704 includes radial cutouts 720, 722 and valve housing 702includes the two corresponding inlet ports 708, 710 that define an openposition such that, when the spool is arranged in the second position(FIG. 3 and FIG. 8D), the third position (FIG. 4 and FIG. 8E), the firstintermediate position (FIG. 5 and FIG. 8B), and the second intermediateposition (FIG. 6 and FIG. 8D), and pump 34 is fluidly connected to thefluid circuit via both of the two radial cutouts 720, 722.

When spool 704 is positioned in the first intermediate position (FIG. 5and FIG. 8B), an edge of the inlet of the valve housing for pump 34 isapproximately in line with an edge of a corresponding cutout of thespool such that, despite an approximate line-line position of the twoedges, pressure from pump 34 causes fluid to flow to the fluid circuit.

When spool 704 is positioned in the second intermediate position (FIG. 6and FIG. 8D), an edge of the inlet of the valve housing for the firstpump is approximately in line with an edge of a corresponding cutout ofthe spool such that, despite an approximate line-line position of thetwo edges, pressure from pump 32 causes fluid to flow to the fluidcircuit. Substantially an entire fluid output of pump 34 passes throughthe line pressure valve when spool 704 is arranged in the secondposition (FIG. 3 and FIG. 8C), the third position (FIG. 4 and FIG. 8E),and the second intermediate position (FIG. 6 and FIG. 8D).

FIGS. 9A and 9B illustrate flow metering notches according to twoembodiments. The flow metering notches encourage or enhance fluid flowduring all positions of operation, but particularly with respect to whenthe spool is positioned in its intermediate positions as describedabove. As mentioned, when approximate “line-line” positions occurbetween housing 702 and spool 704, flow occurs, or just begins to occur,which is caused when pressure from the pumps pressurizes the fluid,causing it to pass from the inlet, to the cavities 720, 722, from whichit flows to the respective outlets 712, 714. Similar flow occurs betweeninlet 716 and outlet 718 due to the presence of notches therein, aswell. Thus, disclosed is one or more flow metering notches thatcorrespond to at least one of the inlet ports such that flow through theinlet port is enhanced during axial movement of the spool.

FIG. 9A, in one example, includes flow metering notches 900 that arepositioned within spool 704. FIG. 9B, in another example, include flowmetering notches 902 that are positioned within housing 702 and withinrespective inlets 708, 710, and 716. Accordingly, when spool 704 ispositioned in its intermediate positions (FIG. 5/FIG. 8B, and FIG.6/FIG. 8D) flow begins due to the pressure against the spool due to thepressure from the corresponding pumps. However, flow is enhanced in theintermediate positions due to the cutout of one or more flow meteringnotches 900 that are positioned in the spool 704 (FIG. 9A), and/or oneor more flow metering notches 902 that are positioned in the housing 702(FIG. 9B).

Further, although two flow inlets 708, 710 are illustrated anddescribed, as is one inlet 716 (with corresponding outlets 712, 714,718), it is contemplated that more or less inlets 708, 712 may beprovided that correspond with pump 34, and that more inlets 716 may beprovided that correspond with pump 32. That is, the use of two inlets708, 710 for pump 34, and one inlet 716 for pump 32, are merelyexemplary, and that further flow control may be provided in LPV 58 viaadditional inlets and outlets, as well.

Accordingly, in operation pump 32 is always connected to the HP circuit.The LPV valve regulates whether the first fluid circuit relieves flow tothe low pressure circuit. Pump 34 becomes connected to the HP circuit,which occurs when the pump 34 flow becomes blocked from going to the lowpressure circuit, and the pump pressure increases. This increases thepressure on the outlet of pump 34. When the pressure on pump side ofBACV (pressure at 102) becomes greater than the pressure on the HP sideof BACV (pressure at 104) plus the pressure delta to crack BACV, flowfrom the 2nd pump heads over to the first fluid circuit. As such, theLPV determines whether pump 34 is connected to the LP fluid circuit andhow much restriction it creates to get flow from pump 34 to the LP fluidcircuit. If the restriction is great enough through the LPV, flowtravels through BACV to the first fluid circuit.

It will be appreciated that the exemplary hydraulic system describedherein has broad applications. The foregoing configurations were chosenand described in order to illustrate principles of the methods andapparatuses as well as some practical applications. The precedingdescription enables others skilled in the art to utilize methods andapparatuses in various configurations and with various modifications asare suited to the particular use contemplated. In accordance with theprovisions of the patent statutes, the principles and modes of operationof the disclosed container have been explained and illustrated inexemplary configurations.

It is intended that the scope of the present methods and apparatuses bedefined by the following claims. However, it must be understood that thedisclosed hydraulic system may be practiced otherwise than isspecifically explained and illustrated without departing from its spiritor scope. It should be understood by those skilled in the art thatvarious alternatives to the configuration described herein may beemployed in practicing the claims without departing from the spirit andscope as defined in the following claims. The scope of the disclosedcontainer should be determined, not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. It is anticipated and intended that futuredevelopments will occur in the arts discussed herein, and that thedisclosed systems and methods will be incorporated into such futureexamples. Furthermore, all terms used in the claims are intended to begiven their broadest reasonable constructions and their ordinarymeanings as understood by those skilled in the art unless an explicitindication to the contrary is made herein. In particular, use of thesingular articles such as “a,” “the,” “said,” etc., should be read torecite one or more of the indicated elements unless a claim recites anexplicit limitation to the contrary. It is intended that the followingclaims define the scope of the device and that the method and apparatuswithin the scope of these claims and their equivalents be coveredthereby. In sum, it should be understood that the device is capable ofmodification and variation and is limited only by the following claims.

What is claimed is:
 1. A line pressure valve comprising: a valve housinghaving a central cavity and a plurality of inlet and outlet ports; and aspool positioned within the central cavity and axially displaceabletherein, the spool having a plurality of radial cutouts that fluidlyconnect respective inlet and outlet ports based on an axial position ofthe spool with respect to the valve housing; wherein first and secondpumps are fluidly connectable and disconnectable respectively to andfrom the fluid circuit based on the axial position of the spool via theinlet and outlet ports.
 2. The line pressure valve of claim 1, wherein:the first pump is fluidly disconnected from the fluid circuit when thespool is arranged in a first, a second, and a first intermediateposition between the first and second positions, and the first pump isfluidly connected to the fluid circuit when the spool is arranged in athird position and a second intermediate position between the second andthird positions; and the second pump is fluidly disconnected from thefluid circuit when the spool is arranged in the first position, and thesecond pump is fluidly connected to the fluid circuit when the spool isarranged in the second position, the third position, the firstintermediate position, and the second intermediate position.
 3. The linepressure valve of claim 2, wherein the spool includes two radial cutoutsand the valve housing includes two corresponding inlet ports that definean open position such that, when the spool is arranged in the secondposition, the third position, the first intermediate position, and thesecond intermediate position, the second pump is fluidly connected tothe fluid circuit via both of the two radial cutouts.
 4. The linepressure valve of claim 2, wherein when the spool is positioned in thefirst intermediate position, an edge of the inlet of the valve housingfor the second pump is approximately in line with an edge of acorresponding cutout of the spool such that, despite an approximateline-line position of the two edges, pressure from the second pumpcauses fluid to flow to the fluid circuit.
 5. The line pressure valve ofclaim 4, wherein when the spool is positioned in the second intermediateposition, an edge of the inlet of the valve housing for the first pumpis approximately in line with an edge of a corresponding cutout of thespool such that, despite an approximate line-line position of the twoedges, pressure from the first pump causes fluid to flow to the fluidcircuit.
 6. The line pressure valve of claim 5, further comprising oneor more flow metering notches that correspond to at least one of theinlet ports such that flow through the inlet port is enhanced duringaxial movement of the spool.
 7. The line pressure valve of claim 6,wherein the one or more flow metering notches are cutouts in the spool.8. The line pressure valve of claim 6, wherein the one or more flowmetering notches are cutouts in the valve housing.
 9. The line pressurevalve of claim 2, wherein substantially an entire fluid output of thesecond pump passes through the line pressure valve when the spool isarranged in the second position, the third position, and the secondintermediate position.
 10. The line pressure valve of claim 2, whereinthe line pressure valve is disposed in a fluid path between the firstpump and the second fluid circuit and the second pump and the secondfluid circuit.
 11. A hydraulic system comprising: a first fluid circuit;a second fluid circuit; a first pump fluidly connected to the firstfluid circuit and selectively connectable to the second fluid circuit; asecond pump selectively fluidly connectable to the first fluid circuitand the second fluid circuit; a line pressure valve comprising: a valvehousing having a central cavity and a plurality of inlet and outletports; and a spool positioned within the central cavity and axiallydisplaceable therein, the spool having a plurality of radial cutoutsthat fluidly connect respective inlet and outlet ports based on an axialposition of the spool with respect to the valve housing; wherein thefirst and second pumps are fluidly connectable and disconnectablerespectively to and from the first and second fluid circuits based onthe axial position of the spool via the inlet and outlet ports.
 12. Thehydraulic system of claim 11, wherein: the first pump is fluidlydisconnected from the second fluid circuit when the spool is arranged ina first, a second, and a first intermediate position between the firstand second positions, and the first pump is fluidly connected to thesecond fluid circuit when the spool is arranged in a third position anda second intermediate position between the second and third positions;and the second pump is fluidly disconnected from the second fluidcircuit when the spool is arranged in the first position, and the secondpump is fluidly connected to the second fluid circuit when the spool isarranged in the second position, the third position, the firstintermediate position, and the second intermediate position.
 13. Thehydraulic system of claim 12, wherein the spool includes two radialcutouts and the valve housing includes two corresponding inlet portsthat define an open position such that, when the spool is arranged inthe second position, the third position, the first intermediateposition, and the second intermediate position, the second pump isfluidly connected to the second fluid circuit via both of the two radialcutouts.
 14. The hydraulic system of claim 12, wherein when the spool ispositioned in the first intermediate position, an edge of the inlet ofthe valve housing for the second pump is approximately in line with anedge of a corresponding cutout of the spool such that, despite anapproximate line-line position of the two edges, pressure from thesecond pump causes fluid to flow to the second fluid circuit.
 15. Thehydraulic system of claim 14, wherein when the spool is positioned inthe second intermediate position, an edge of the inlet of the valvehousing for the first pump is approximately in line with an edge of acorresponding cutout of the spool such that, despite an approximateline-line position of the two edges, pressure from the first pump causesfluid to flow to the second fluid circuit.
 16. The hydraulic system ofclaim 15, further comprising one or more flow metering notches thatcorrespond to at least one of the inlet ports such that flow through theinlet port is enhanced during axial movement of the spool.
 17. Thehydraulic system of claim 16, wherein the one or more flow meteringnotches are cutouts in the spool.
 18. The hydraulic system of claim 16,wherein the one or more flow metering notches are cutouts in the valvehousing.
 19. The hydraulic system of claim 12, wherein substantially anentire fluid output of the second pump passes through the line pressurevalve when the spool is arranged in the second position, the thirdposition, and the second intermediate position.
 20. The hydraulic systemof claim 12, wherein the line pressure valve is disposed in a fluid pathbetween the first pump and the second fluid circuit and the second pumpand the second fluid circuit.